1. Field of the Invention
The present invention relates to Poly(2-Octadecyl-Butanedioate) (and the corresponding acid, Poly(2-Octadecyl Butanedioic Acid)) and more particularly pertains to the use of Poly(2-Octadecyl-Butanedioate) and Poly(2-Octadecyl-Butanedioic Acid) as Chelating Compounds. The Method of Using Poly(2-Octadecyl-Butanedioate) and Poly(2-Octadecyl-Butanedioic Acid) for Chelating purposes is described herein.
2. Description of the Prior Art
The use of chelating agents is known in the prior art. More specifically, chelating agents previously devised and utilized for the purpose of binding heavy metals are known to consist basically of familiar, expected, and obvious structural configurations, and chemical compounds, notwithstanding the myriad of designs encompassed by the crowded prior art which has been developed for the fulfillment of countless objectives and requirements.
By way of example, compounds used to remove heavy metals from aqueous solutions can be classified in to two general categories, heterogeneous and homogeneous. Heterogeneous materials are insoluble in water and are characterized by slow binding kinetics and low adsorption capacities. Homogeneous materials are soluble in water, have high binding kinetics and relatively high adsorption capacities. For example, Geckeler K, Lange G, Eberhardt H, Bayer E authored Preparation and Application of Water-Soluble Polymer-Metal Complexes, found in Pure & Appl. Chem 52:1883-1905 (1980). These authors state that insoluble chelating resins have considerable disadvantages, such as reaction in heterogeneous phase and long contact times.
In general, there are three requirements with which polymers as chelating agents should comply; (1) sufficient solubilizing power of the constitutional repeating unit which provides water-solubility of the polymer complexes, (2) a great number of functional groups of the complexing agent for a high capacity, and (3) a high molecular weight which allows an easy separation by usual methods from the metal not bound to the polymer.
Water-solubility is provided by a high content of hydrophilic groups, e.g. amino, hydroxyl, carboxyl, amide and sulfonic acid groups, or hydrophilic units of the polymer backbone (ether or imino groups).
Bhattacharyya D, et al. in U.S. Pat. No. 6,544,418, teaches IERs (ion exchange resins), such as strong acid or weak acid cationic exchangers, have been used extensively to recover heavy metals and/or prepare high quality water. The typical theoretical capacity of these IERs is five meq/gram. This capacity is quite low. For Ni(II), a maximum uptake of only 0.15 grams of metal per gram of IER is possible. Several specific examples are given below.
Heterogeneous Separations
Chelating Resins
Park I H and Kim K M. authored Preparation of Chelating Resins Containing a Pair of Neighboring Carboxylic Acid Groups and the Adsorption Characteristics for Heavy Metal Ions. The article was published in Sep Sci and Tech, 40:2963-2986 (2005).
These authors reported adsorptivities of 0-52 mg metal/gram resin for their malonic acid polymer. The resins reported herein had adsorptivity (mg metal/gram resin), depending upon the carboxylic acid content, of:                1. Pb(II) 17.71-52.21        2. Hg(II) 9.62-40.26        3. Cu(II) 20.44-25.73        4. Cd(II) 17.19-46.88        5. Ni(II) 4.16-10.56        6. Co(II) 16.07-31.82        7. Cr(III) 0.00-2.25        
The above results were obtained only after a very long incubation defined as 28 hr incubation at 20 degrees C. and a pH of 5.
Bruening, R L, et al., disclosed in International Patent Application Number PCT/US92/02730 the production of chelating polymers formed from polyalkylene-polyamine-polycarboxylic acid ligands covalently bonded through a spacer group to a silicon atom and further covalently bonded to a solid support.
The above series of polymers is different from that described in the current invention for several reasons.
(1) The carboxylate or carboxylic acid functional groups in the above series are not located on adjacent or nearly adjacent carbon atoms in the polymer backbone.
(2) The polymer backbone contains amine functionality. The non-bonding electron pairs located on these nitrogen atoms may contribute to the chelation ability of these polymers, and will contribute to the three-dimensional conformation of the polymer. Nitrogen atoms are not present in the polymer described in the current invention.
(3) The carboxylate or carboxylic acid groups are attached to the polymer backbone by pendent chains containing at least one carbon atom. The carboxylate or carboxylic acid groups in the polymer described in the current invention are directly attached to the polymer chain. (For the reported importance of pendent chains as described in the literature see Yamaguchi, U.S. Pat. No. 6,107,428 below.)
Unlike the prior art, the carboxylate or carboxylic acid groups in the current invention are directly attached to the polymer backbone. These carboxyl groups may be two, three, or four or more carbons away from each other on the backbone. This structure allows the backbone to potentially close on itself, forming a transient non-covalently-bound ring structure. In this way, the ring potentially determines the size of the molecule or ion that it can chelate within that ring. The larger the ring, the larger the molecule or ion. More importantly, the use of ring size to selectively determine the molecule or ion that will be chelated will allow the user to decide which molecule or ion it wishes to have chelated, leaving smaller or larger molecules or ions in the solution.
Hydrogels
Katime I. and Rodriguez E., authored Absorption of Metal Ions and Swelling Properties of Poly(Acrylic Acid—Co-Itaconic Acid) Hydrogels in J. Mactomol. Sci. —Pure Appl. Chem., A38(5&6), 543-558 (2001).
The above authors investigated the binding properties of insoluble hydrogels and found the process to be very slow, as polymer swelling for 100-1000 minutes is required prior to metal adsorption. Additionally, the rate is limited by metal diffusion inside the hydrogel and hydrogel-water interfacial area and desorption is slow, requiring 2 days in a 0.1M sulfuric acid solution.
Ion-Exchange Membrane
Sengupta S, and Sengupta A K. authored Characterizing a New Class of Sorptive/Desorptive Ion Exchange Membranes for Decontamination of Heavy-Metal-Laden Sludges. Their paper was published in Environ. Sci. Technol. 1993, 27, 2133-2140.
The authors produced selective chelating exchangers physically enmeshed or trapped in thin sheets of highly porous poly(tetrafluoroethylene) (PTFE).
A cation exchanger, having the chemical formula (R—CH2—N(CH2COOH)2), contains nitrogen functionality.
The cation described above is crosslinked with divinylbenzene, making R the styrene monomer. The polymer matrix (R) is covalently attached to the chelating iminoacetate functional group.
In kinetic studies, Pb+2 concentration went from 210 mg/L to 125 mg/L in 450-500 minutes (about 8 hours) indicating that this solid phase extraction is slow.
Bhattacharyya D, et al., in U.S. Pat. No. 6,544,418, described a method to prepare and regenerate a composite polymer and silica-based membrane. The researchers attached a polyamino acid to the silica-based membrane by reacting a terminal amine group of the polyamino acid with one of the epoxide groups on the membrane.
Capacity of these membranes in g Pb/g resin are as follows: poly-L-aspartic acid=0.12;
poly-L-glutamic acid=0.30.
These capacity levels are approximately 10 times conventional ion-exchange/chelation sorbents. The authors stated that the polyamino acid functionalization is critical for this effect. The Incubation time is about 1-2 hours.
Films
Philipp W H, et al., in U.S. Pat. No. 5,371,110, discloses the production of films comprised of a poly(carboxylic acid) supported in a water insoluble polymer matrix poly(vinyl acetal). The polymer is made by treating a mixture made of poly(vinyl alcohol) and poly(acrylic acid) with a suitable aldehyde and an acid catalyst to cause acetalization with some cross-linking. The reaction with the aldehyde (1) locks in the poly(acrylic acid) so that the poly(carboxylic acid) can no linger be removed from the polymer by water and (2) makes the film insoluble in water (by cross-linking). The results are given below:
Initial [Pb]=16.37 ppm,
Final [Pb]=1.44 ppm (91% removal)
24 hour incubation.
Davis H, et al., in U.S. Pat. No. 3,872,001, developed a porous film capable of removing heavy metal pollutants from aqueous media. Reacted with the acid groups in the polymeric film backbone is a chelate (such as EDTA), capable of forming a complex with the heavy metal pollutants to be removed from the aqueous media.
The most preferred among the chelating agents is EDTA and this procedure removed from 55-95% of mercury and cadmium from the solution.
Biosorption
Davis T A, Volesky B, and Mucci A., in Water Research 37 (2003) 4311-4330, provide a review of the biochemistry of heavy metal biosorption by brown algae.
Brown algae biomass is a reliable and predictable way to remove Pb+2, Cu+2, Cd+2 and Zn+2 from aqueous solutions. This is due in part to the specific structural conformations of various polysaccharides in the algae. Without this specific structural arrangement, binding would not occur. Specifically, alginic acid or alginate, the salt of alginic acid, is the common name given to the family of linear polysaccharides containing 1,4-linked B-D-mannuronic (M) and alpha-L-guluronic (G) acid residues arranged in a non-regular, blockwise order along the chain. The residues typically occur as (-M-)n, (-G-)n and (-MG-)n sequences or blocks, where “n” is an integer. The carboxylic acid dissociation constants of M and G have been determined as pKa=3.38 and pKa 3.65, respectively, with similar pKa values for the polymers.
Polymannuronic acid is a flat ribbon-like chain, its molecular repeat unit contains two diequitorially linked beta-D mannuronic acid residues in the chair conformation. In contrast, poly guluronic acid contains two diaxially linked alpha-L-guluronic acid residues in the chair form which produces a rod-like polymer. This key difference in molecular conformation between the two homopolymeric blocks is believed to be chiefly responsible for the variable affinity of alginates for heavy metals.
The higher specificity of polyguluronic acid residues for divalent metals is explained by its “zigzag” structure which can accommodate the Ca+2 (and other divalent cations) ion more easily. The alginates are thought to adopt an ordered solution network, through inter-chain dimerization of the polyguluronic sequences in the presence of calcium or other divalent cations of similar size. The rod-like shape of the poly-L-guluronic sections results in an alignment of two chain sections yielding an array of coordination sites, with cavities suitable for calcium and other divalent cations because they are lined with the carboxylate and other oxygen atoms of G residues. This description is known as the “egg-box” model.
With alginates, the preferential binding of heavier ions was attributed to stereochemical effects, since larger ions might better fit a binding site with two distant functional groups. Additionally, the key to binding in alginates appears to be the orientation of the oxygen atoms with respect to the —COO— group. In guluronic acid the ring oxygen and the axial 0-1 form a spatially favorable environment with —COO—, and opposed to the equatorial.
Homogeneous Separations
Water Soluble Polymers
Rivas B. L. and Pereira E. authored Functional Water Soluble Polymers with Ability to Bind Metal Ions, publishing their work in Macromol. Symp. 2004, 216, 65-76. Rivas B L. and Schiappacasse L N. authored Poly(acrylic acid-co-vinylsulfonic acid): Synthesis, Characterization, and Properties as Polychelatogen, publishing their work in J. Appl Polym Sci, 88: 1698-1704 (2003).
Water-soluble polymers (WSP) containing ligands at the main or side chains have been investigated for the removal of metal ions in the homogeneous phase. These chelating polymers are termed polychelatogens. The authors state that among the most important requirements for technological aspects of these polymers are their high solubility in water, easy and cheap route of synthesis, and adequate molecular weight and molecular weight distribution, chemical stability, high affinity for one or more metal ions, and the selectivity for the metal ion of interest.
Also taught is that polyelectrolytes may be distinguished from chelating polymers. The former have charged groups, or easily ionizable groups in aqueous solution, while the latter bears functional groups with the ability to form coordination bonds.
Membrane filtration processes can be successfully used for the separation of inorganic species and for their enrichment from dilute solutions with the aid of a water-soluble polymer. This technique is called the liquid-phase polymer based retention, or “LPR” technique.
The main features of a liquid-phase polymer-based retention system are a membrane filtration, reservoir and a pressure source, such as a nitrogen bottle.
Another separation technique involves the removal of metal ions from aqueous solutions by means of complexation with a water-soluble polymer followed by ultrafiltration (UF).
The kinetics of chelation may be time sensitive and require several hours, up to “overnight”, depending upon the characteristics of the water-soluble polymer.
These water-soluble polymers form the most stable complexes at pH=5, retaining between 70-75% of Cu(II), Cd(II), Co(II), Ni(II), Zn(II), and Cr(III).
At high ionic strength (0.1M NaNO3), for both Ni(II) and Cu(II), the polychelatogens show a low retention capacity (<10%). This can be explained by the shielding effect of the single electrolyte (in excess) on the charge of the polyion. By decreasing the single electrolyte concentration (0.01M NaNO3), the behavior changes sharply (45-90% retention depending upon the ion).
Smith, et al., in U.S. Pat. No. 5,766,478, reported a water soluble polymer capable of binding with the target metal, where a polymer metal complex is formed and separated by ultrafiltration.
All polymers thus formed contained nitrogen functional groups or were crown ether derivatives. These polymers demonstrated a 30 minute incubation time.
The Limitations of Carboxylate and Carboxylic Acid Chelating Groups, as Described in the Literature
Bhattacharyya D, et al. in U.S. Pat. No. 6,544,418, indicate that the polyamino group is a better chelator than the poly carboxylic acid group.
Various sorbents/ion exchange materials are available for metal ion sequestration. Unfortunately, however, all of these suffer from the disadvantage that they possess at most two or three functional groups capable of ion interaction per attachment site.
Capacity of these membranes in g Pb/g resin are as follows:
poly-L-aspartic acid=0.12;
poly-L-glutamic acid=0.30.
These capacities are approximately 10 times conventional ion-exchange/chelation sorbents. Authors state that the polyamino acid functionalization is critical for this effect.
Rivas B L, Pooley S A, Soto M, Aturana H A, Geckeler K E authored Poly(N,N′-dimethylacrylamide-co-acrylic acid): Synthesis, Characterization, and Application for the Removal and Separation of Inorganic Ions in Aqueous Solution, published in J. Appl Polym Sci 67: 93-100 (1998)
The authors indicate that the polyamino group is a better chelator than the polycarboxylic acid group, in that incorporation of amide functionality into a soluble poly carboxylic acid improved ion retention to 88-90% (from 60-70%) for all of the above ions except for Pb(II), which stayed at 50%.
W. F. McDonald, in U.S. Pat. No. 6,495,657, disclosed that polyamides are preferred over polycarboxylic acids for the binding of heavy metals. Polyamides are effective heavy metal catalysts because of the two-dimensional structure of the backbone. Amides are known to exist in a partial double bond configuration, thereby making the structure of the polymer backbone a series of two-dimensional planes with limited rotation between them. This structural configuration is said to enhance binding and utility. Furthermore, the patentee states that varying the amine used to form the amide can further alter the utility and binding characteristics of the polymer. In the current invention, the absence of nitrogen in the backbone prevents the formation of double bonds. All of the carbon bonds in the polymer backbone are able to freely rotate. The prior art above teaches that limiting conformations enhances binding and utility. In the current invention, increasing conformations is shown to enhance binding and utility.
Yamaguchi, in U.S. Pat. No. 6,107,428, discloses that carboxylic acid groups must have free rotation and not be inhibited by the polymer backbone in order to be effective chelators. Thus, these authors teach that the carboxylic acid group(s) can not be directly bonded to the polymer backbone.
In the polymers based on carboxylic acids produced by polymerizing a monomer of maleic acid or acrylic acid, a carboxyl group bonds directly to the main chain, and for this reason, the main chain inhibits free rotation of the carboxyl group. Thus, such polymers based on carboxylic acids render unsatisfactory ability in capturing metal ions, especially heavy metal ions. The authors found a polymer having the desired structure that is soluble in water and has a high ability to capture heavy metal ions. The monomer has a molecular structure having a plurality of carboxyl groups bonded away from the double bond. Accordingly, the polymer has a molecular structure including a plurality of carboxyl groups which are not directly bonded to the main chain, and for this reason, free rotation of carboxyl groups is not inhibited by the main chain. Thus, the polymer is soluble in water and compared with conventional chelating agents, renders an excellent dispersing effect on inorganic particles and a high ability to capture heavy metal ions.
Park I H. and Kim K M. authored Preparation of Chelating Resins Containing a Pair of Neighboring Carboxylic Acid Groups and the Adsorption Characteristics for Heavy Metal Ions, published in Sep Sci and Tech, 40:2963-2986 (2005). Authors state that better performance is obtained when the carboxylic acid groups are not directly bonded to the polymer backbone. In this study, two different kinds of short/long malonic acid pendant groups were added to a chelating polymer backbone in order to optimize the adsorptivity toward heavy metals. The authors prepared chelating resins containing a pair of carboxylic acid groups. In all cases, these were separated by a benzene ring and two methylene groups or two methylene groups from the polymer backbone. Additionally, both carboxylic acids were attached to the same carbon. The resins with spacer units among pendant chelating groups were more accessible for the adsorption of heavy metal ions than those without spacers, and the intervals between a pair of neighboring chelating groups had been also controlled for the effective adsorption of heavy metal ions. The adsorption capacities of chelating resins containing carboxylic acid groups toward heavy metal ions are generally low. The authors report optimal adsorption capacities of 18-52 mg/g for their poly carboxylic acids. This is significantly less than the 290 mg/g observed for the invented polymer.
Davis T A. Volesky B. and Mucci A. authored A Review of the Biochemistry of Heavy Metal Biosorption by Brown Algae, published in Water Research 37 (2003) 4311-4330. The authors state that the three-dimensional conformation of the chelator is important. The authors also state that functional groups responsible for the chelation should preferably be distant from each other. The higher specificity of polyguluronic acid residues for divalent metals is explained by its “zigzag” structure which can accommodate the Ca+2 (and other divalent cations) ion more easily. The alginates are thought to adopt an ordered solution network, through inter-chain dimerization of the polyguluronic sequences in the presence of calcium or other divalent cations of similar size. The rod-like shape of the poly-L-guluronic sections results in an alignment of two chain sections yielding an array of coordination sites, with cavities suitable for calcium and other divalent cations because they are lined with the carboxylate and other oxygen atoms of G residues. This description is known as the “egg-box” model. With alginates, the preferential binding of heavier ions was attributed to stereochemical effects, since larger ions might better fit a binding site with two distant functional groups.
Park I-H. Rhee, J. M., and Jung, Y. S. authored Synthesis and Heavy Metal Ion Adsorptivity of Macroreticular Chelating Resins Containing Phosphono and Carboxylic Acid Groups, published in Die Angewandte Makromolekulare Chemie (1999) 27-34. The authors state that the adsorption ability of chelating resins containing only carboxylic acid groups toward heavy metals was very low. As a result, various improved resins containing dithiocarbamates, aminomethyl phosphoric acid groups, amidooximes, imidazoles, mercaptoamines, diphosphonates, and phosphono groups have been prepared. Adsorption capacities for these improved resins were still very low, only averaging about 2 mg/g resin. (By comparison, the polymer described in this invention had adsorption capacities 150 times greater.)
In summary, the characteristics of this polymer are not predicted by the literature and, as such, the use of the polymer to carry out chelation in the manner described, is unexpected, and constitutes a new and unexpected use for the polymer. Contrary to the literature that teaches that this polymer should not work in the manner shown empirically, it has been demonstrated that the polymer, as herein described, functions in a new, unanticipated manner.
While these compounds disclosed in the prior art fulfill their respective, particular objectives and requirements, the aforementioned patents and prior art do not describe the Chelating Compounds, and the Method of Use of Poly(2-Octadecyl-Butanedioate) and Poly(2-Octadecyl-Butanedioic Acid) that allows the use of re-usable compounds for binding and removing heavy metals from a solution.
In this respect, the Chelating Compounds, and Method of Use of Poly(2-Octadecyl-Butanedioate) and Poly(2-Octadecyl-Butanedioic Acid) according to the present invention substantially departs from the conventional concepts and compounds described in the prior art, and in doing so provides compounds primarily developed for the purpose of providing re-usable compounds for binding and removing heavy metals from a solution.
Therefore, it can be appreciated that there exists a
continuing need for new and improved Chelating Compounds, and Method of Use of Poly(2-Octadecyl-Butanedioate) and Poly(2-Octadecyl-Butanedioic Acid) which can be used in a re-usable fashion for binding and removing heavy metals from a solution. In this regard, the present invention substantially fulfills this need.